Seismic Source Characteristics of Nine Strong Earthquakes from 1988 to 1990 and Earthquake Activity since 1970 in the Sichuan-Qinghai-Xizang (Tibet) Zone of China

The Chinese provinces of Sichuan, Qinghai and Xizang (Tibet) are situated in a very active seismic zone. From 1988 to 1990, nine strong earthquakes (M\5.9) occurred in these provinces. A method of analyzing seismic waveforms using apparent source time functions (aSTF) and apparent time differences (aTD) is adopted to derive rupture characteristics for the strong earthquakes. Combining the source characteristics with aftershock data, regional tectonics and geology, this paper examines the migration of strong earthquakes. The Qinghai earthquakes in this study were found to have strong reverse-slip faulting, which is different from the strike-slip focal mechanisms of past earthquakes in the region. The steepness of compressional axes of Sichuan earthquakes is related to the local complicated tectonics. Finally, the single-link cluster (SLC) method is used to analyze the spatial-temporal behavior of the all strong earthquakes that occurred in the region since 1970. The SLC analysis suggests that the patterns of earthquake activity can be identified well and that continental earthquakes occur seemingly with basic regularity.